Prior Art
Industry has been using N,N-bis(hydroxyethyl)-N-alkylamines for a long time because of their antistatic properties and, preferably, their C.sub.16 -C.sub.20 alkyl derivatives, in particular, N,N-bis(hydroxyethyl)-N-stearylamine or the corresponding technical derivatives with a tallow or hydrogenated tallow chain. However, the antiacid function, which assures stability to heat and light of chlorinated polymers or nonchlorinated polymers but which requires halogenated catalysts of the Ziegler type for their polymerization, has been widely based on magnesium oxide (magnesia MgO) and on basic magnesium and aluminum carbonate, hydrotalcite, RN=12304-65-3, MgCO.sub.3.5Mg(OH).sub.2.2Al(OH).sub.3.4H.sub.2 O (referred to below as HTal), substances the antiacid properties of which are well known and utilized in various fields, for example, in the pharmaceutical field. Therefore, it was desirable to combine these two types of components in one flake additive formulation. When doing this, two types of difficulties are encountered. The first ones relate to the difficulty of producing the flakes on the flaking equipment and the second is the appearance and behavior of the flake-form products.
The additives in question are intended to produce additive/polymer stock mixtures. Their presentation in the form of flakes is very valued. Evidently, these flakes should be able to be melted and be stable at the temperature of manufacture of these stock mixtures, which is hardly any problem. It is also necessary that they do not produce any dust during handling and that they do not agglomerate during somewhat prolonged storage. These are the properties which are more or less needed, in combination with the characteristics required for a correct flake-form product. The simple ethoxylated amines/magnesium oxide and/or hydrotalcite compositions do not satisfy these requirements. The present invention remedies these disadvantages.
We shall recall briefly as to what constitutes a flaking equipment. The device essentially consists of a flaking roll in immediate contact with an inking roll of smaller diameter, which is immersed into a trough in which the product to be flaked is maintained in the molten form, around 80.degree. C. in the case of the additives according to the invention. The inker turns in a direction opposite to the flaker and deposits on it a thin and uniform layer of the product. The flaker is maintained at a temperature 15 to 20.degree. C. below the solidification point of the product to be flaked. A solidified film is formed on it, which is taken off with a doctor blade. The debris is sent to a grinding/lump-breaker system from which the flakes are then directed toward the packaging workshop.
We shall emphasize the following among the most frequent incidents during flaking:
Separation in the Trough:
The physical constituents of the formulation of the additive are separated and the flakes then will no longer be homogeneous. The phenomenon becomes more severe as the time of operation continues and it may lead to stopping the flaking operation.
The Flaking Film Sticks.
The mixture is homogeneous, but the film formed on the flaker is ductile and/or sticking. Scraping becomes defective or impossible. The flakes, even if they form, have a pronounced tendency to form lumps.
Formation of Fines.
Multiple causes. For example, the film formed is too thin because the composition was too fluid, was scraped in plaques and ground into too fine particles. The final product is incorrect, with a tendency of lumping, and above all, unacceptable unhealthiness of the workshop.
Therefore, a flakable composition should have a melting point located between 40 and 80.degree. C. for reasons of flaking, but also because of utilization. In practice, the minimum melting point is set at 44.degree. C. Thus, the low melting point of the ethoxylated amine (39.degree. C. for the hardest one, the ethoxylated amine of hydrogenated tallow) should be compensated which is done by the addition of a mineral filler. It was found, and a part of the invention utilizes this observation, that one cannot harden the mixture at will by increasing the amount of filler. Beyond a certain amount, the molten mixture is no longer homogeneous and separates in the trough or in the inking bath. The flakes will then no longer have a homogeneous composition; they will form an island of waxy material with an excess of ethoxylated amine and become sticky. Thus, there is a practical limit to the amount of filler, which is around 15% by weight. In the additives of the invention, this role of the filler, to be active toward hydrochloric acid, is assigned to the magnesium hydroxide or to the hydrotalcite. It is found that, from this point of view, these substances are particularly difficult to use and, in order to assure homogeneity of the formulation, it is necessary to include a stabilizer, which evidently should be compatible with the polymers. This necessitates an additive for making the stock mixtures moldable or extrudable. Calcium stearate is used for this purpose. Here, one is again limited to an amount which should be below 25% of the stearate or otherwise the flakes become sticky.